C++ Programming/Code/Standard C Library/Functions/perror

perror #include <cstdio> void perror( const char *str ); The perror() function writes str, a ":" followed by a space, an implementation-defined and/or language-dependent error message corresponding to the global variable errno, and a newline to stderr. For example: char* input_filename = "not_found.txt"; FILE* input = fopen( input_filename, "r" ); if( input == NULL ) { char error_msg[255]; sprintf( error_msg, "Error opening file '%s'", input_filename ); perror( error_msg ); exit( -1 ); } If the file called not_found.txt is not found, this code will produce the following output: Error opening file 'not_found.txt': No such file or directory If "str" is a null pointer or points to the null byte, only the error message corresponding to errno and a newline are written to stderr. Related topics clearerr - feof - ferror